Heart failure (HF) is a major clinical problem, with 1 million new cases per year, 1 million annual hospital admissions, a 50% 5-year mortality, and a role in 1 of 8 deaths. Little improvement in these statistics over recent decades indicates that current HF drugs could be improved. A classic feature of HF is elevation of cardiac sympathetic activity and circulating catecholamines, norepinephrine (NE) and epinephrine (EPI). NE and EPI activate 3 types of adrenergic receptors (ARs) on cardiac myocytes, ?1, ?1A, and ?1B. Inhibition of excess, chronic ?1 stimulation with beta-blockers is a key HF treatment, but the mechanisms of beta-blockers are incompletely understood, and there are no approved HF drugs that target ?1-ARs. The overall goals of this project are to uncover novel adrenergic mechanisms in HF, and to further validate ?1A adrenergic agonists as potential new drugs to treat HF. This project builds on 3 important novel findings from recent work. First, published data show that stimulation of an ?1A-ERK pathway with drug agonists can treat HF in mouse models. Second, preliminary data suggest that beta-blockers can rescue NE and EPI activation of ?1A-ERK cardioprotective signaling in cardiac myocytes. Third, published data show a novel model of ARs in ventricular myocytes, where all cells have the ?1 and ?1B, but only a 60% subset have the ?1A, with high levels in only 20%. The ?2 and ?3 ARs are mostly absent in myocytes. Published data also show that ?1-AR knockout decreases myocyte ?1 ARs. These new findings raise several key questions regarding adrenergic mechanisms in HF: First, do beta-blockers work in part by rescuing ?1A-ERK cardiorotective signaling by NE and EPI? Second, as a corollary, is the ?1A receptor required for cardioprotection by beta-blockers? Third, what happens to myocyte ?1 receptors downregulated in HF? Are ?1 receptors lost selectively in the myocytes that do not have the ?1A, and do ?1A receptors protect or maintain ?1 receptors? Fourth, if beta-blockers work in part by enhancing ?1A-ERK signaling by endogenous NE and EPI, will an exogenous ?1A agonist still have efficacy in the presence of a beta-blocker? Four specific aims are proposed to address these key questions: Aim I: Test the hypothesis that beta-blockers rescue ?1A-ERK cardioprotective signaling by NE and EPI. We will use isolated ventricular myocytes from wild type (WT) and ?1A knockout (KO) mice with HF from pressure overload transverse aortic constriction (TAC), and will examine a PKA-PP2A mechanism. Aim II. Test the hypothesis that cardiac myocyte ?1A receptors are required for ?-blocker efficacy in heart failure. We will compare beta-blocker rescue of TAC HF in WT and induced cardiac myocyte-specific ?1A KO mice. Aim III: Test the hypothesis that ?1A receptors protect ?1-ARs in heart failure. We will use RT- qPCR to quantify ?1A and ?1 mRNAs in individual ventricular myocytes from TAC hearts. RNA sequencing will test a cardioprotective gene profile in ?1A-expressing myocytes. Aim IV: Test the hypothesis that ?1A agonist therapy adds efficacy to beta-blockade in heart failure. We will test the beta-blocker metoprolol in the absence or presence of the specific ?1A agonist A61603 in a rescue protocol where treatment is started late after TAC, when cardiac function is reduced. RNA sequencing will test for differences in gene profiles with single and combined therapy. Successful completion of these Aims will uncover new adrenergic mechanisms in HF therapy, will provide crucial preclinical validation of a potential novel HF therapy with an ?1A agonist, and will hopefully accelerate the translation to patients.